A number of enzymes active in detoxification appear to be characterized by broad specificity and, sometimes, by multiple functions. The glutathione transferases from mammalian liver are active in catalyzing an enormous number of reactions which involve the glutathione thiolate ion, as binding proteins for compounds such as bilirubin and heme; and form covalent complexes with electrophilic reagents including carcinogens. Exploratory work with thiol S-methyltransferase and a number of sulfotransferases, all from rat liver, suggest that the homogeneous enzymes that have been isolated are each able to catalyze reactions with a broad class of compounds.